1. Field of the Invention
This invention relates to a base for a kiln car for use in the firing of ceramic ware.
2. Description of the Prior Art
Such kiln cars conventionally comprise a wheeled trolley made of metal, a heat resistant base mounted on the trolley, an open sided region known as a flue disposed above the base and a refractory superstructure to support the ware. This invention is concerned with the construction of the heat resistant base.
A conventional such base is made of fire bricks cemented together into a solid mass. This construction has been favoured in the past because the fire bricks are adequate insulators to prevent heat generated in the upper part of the kiln, particularly the flue, from having a harmful effect on the metal trolley but also because the fire bricks can carry the quite considerable load of the super structure and the ware loaded on it.
Unfortunately, alongside these advantages, the conventional arrangement has a grave disadvantage in that the base has a very high thermal mass and hence absorbs a considerable amount of the heat generated in the kiln which is therefore not operated as efficiently as it could be.
It has previously been proposed to produce a low thermal mass kiln car base but difficulties have been encountered and expense has been involved in the construction of such a base because of the need for a peripheral heat seal around each kiln car to prevent radiant heat from the burners passing down to the wheeled metal trolley. A solid fire brick base is provided with a step at one end and an overhang at the other end so that, when a number of kiln cars are moved into a kiln, the step and overhang of the adjacent cars overlap and radiant heat cannot be directed downwardly through the gap. Similarly, each side edge of the kiln car base has a projection extending outwardly along its entire length and this projection is received by a groove extending along the side wall of the kiln to form a lateral heat seal between the kiln car and the kiln walls.
It is not necessary to form an air tight seal because heat transfer by conduction through air is negligible and, since the hottest region of the kiln is the flue which is disposed above the base, convection also pays a negligible part in heat transfer. All that is required is a barrier against the penetration of radiant heat from the flue to the wheeled metal trolley, in other words to provide a light-tight seal.
It has previously been proposed to form a low thermal mass base for a kiln car but there has been a problem in providing a heat seal between one car and the next and between the sides of the car and the kiln walls. This has necessitated such extreme measures as casting a complete peripheral surround of a mouldable concrete material which is very skilled work and which is expensive to carry out. Any damage to part of this concrete surrounding structure means that the entire structure has to be replaced and it does have a fairly considerable thermal mass.